The purpose is students to have an idea for the sizes of stars and the relation between the size, mass and the position on the Hertzsprung-Russell diagram.

Necessary materials

• plasticine with different colors: red, yellow, blue, white, black,

• plastic board to work on,

• the image of the Hertzsprung-Russell diagram from the theoretical part.

Instructions for the teacher

This exercise will show the students that the stars are located on the diagram not randomly but in a certain way according their masses, radii, colors and evolutionary status. The duration of the exercise is 10 to 15 minutes.

Detailed instructions for the students

1. Take a look the picture from the theoretical part with Hertzsprung-Russell diagram. Look how the stars are positioned according their colors and sizes on it.

2. Draw a rectangle witj the plasticine as the Y-axis is in black and the X-axis make a rainbow starting with blue, then white, yellow and red. This will give you the limits of the diagram.

3. Start to build the Main sequence with blue balls in the upper left corner of your diagram.

Continue with diagonally with white balls around the middle, then yellow ones and red at the end. Follow the requirements the balls to decrease their size in this order. Mark the place of the Sun on the Main sequence.

4. Make bigger blue balls and place them above the Main sequence at the middle of X-axis – these will be the supergiants. On the left of them and a little below on Y-axis place red balls. These are the giants.

5. And finally at the down left corner place small white balls – this is the region of the white dwarfs.


1. Does the duration of the star on the Main sequence depend on the stellar mass? How? – [Answer: Yes. More massive the star shorter stay on the Main sequence]

2. Show the position of th eSun on the Hertzsprung-Russell diagram. – [Answer: the Sun is placed in the region of yellow dwarfs on the Main sequence.]

3. Do stars continue to be born now? – [Answer: Yes, the process of stars formation continues now.]

4. Which stars live longer – the red giants or the blue giants? Why? – [Answer: The red giants. Because they have smaller mass and spend more slowly the hydrogen in their core.]